Dopamine pre-treatment impairs the anti-cancer effect of integrated stress response- and TRAIL pathway-inducing ONC201, ONC206 and ONC212 imipridones in pancreatic, colorectal cancer but not DMG cells
ONC201 (originally identified as TRAIL-Inducing Compound #10 or TIC10) and its analogue ONC206 have been shown to trigger an integrated stress response, with proposed primary mechanisms involving mitochondrial protein ClpP and antagonism of dopamine receptors D2/3 (DRD2/3). We hypothesized that dopamine, a DRD2 agonist, might counteract the effects of ONC201 or ONC206 by competing for DRD2/3, thereby reducing their anti-cancer efficacy and protecting tumor cells from their cytotoxic impact. To test this, we pre-treated cancer cells from various origins—including breast, pancreatic, colorectal cancer, and diffuse midline glioma (DMG)—with dopamine, followed by treatment with ONC201, ONC206, or ONC212. After 48 hours, we found that dopamine pre-treatment reduced the ability of ONC201, ONC206, and ONC212 to suppress cell viability in pancreatic and colorectal cancer cells. Further, we conducted colony formation assays by pre-treating multiple cancer cell lines with dopamine for a week before exposing them to ONC201, ONC206, or ONC212. Dopamine pre-treatment impaired the anti-cancer effects of ONC201 and ONC206 in pancreatic and colorectal cancer cells. While ONC212’s effect was also impaired in colorectal cancer cells, no such impairment was observed in pancreatic cancer cells in the colony assay. Additionally, no protection from imipridone-induced cell death was seen when tumor cells were pre-treated with the DRD2 agonist sumanirole, nor in brain tumor cell lines pre-treated with dopamine. To explore the molecular basis of this effect, immunoblotting was performed to examine whether dopamine pre-treatment altered key signaling pathways influenced by ONC201. The results showed no effect on ATF4, CHOP, DR5, or ClpX expression, all of which are affected by ONC201. Instead, the reduced efficacy of ONC201, ONC206, and ONC212 following dopamine pre-treatment appeared to be associated with the upregulation of anti-apoptotic proteins such as p-Bad, XIAP, FLIP, and pAkt. These findings highlight dopamine’s potential role in protecting cancer cells from imipridone treatment, the variability across different tumor types, and suggest that dopamine’s impact on tumor cell survival may occur through pathways independent of DRD2 receptor expression.